Methods, apparatus and systems for biometric processes

ABSTRACT

Described embodiments relate to a method operable in a biometric authentication system. The method comprises initiating generation of an acoustic stimulus for application to a user&#39;s ear; and determining a quality measure of a response signal to the acoustic stimulus. Responsive to determining that the quality measure is inadequate for performing a biometric process, the method comprises one or more of: (i) modifying one or more properties of the acoustic stimulus to improve a signal to noise ratio, SNR, of the response signal and (ii) cancelling the effect of noise from outside the ear on the response signal of the user&#39;s ear to the acoustic stimulus to improve the SNR of the response signal.

TECHNICAL FIELD

Embodiments of the disclosure relate to methods, apparatus and systemsfor biometric processes, and particularly to methods, apparatus andsystems for improving biometric processes involving the measuredresponse of a user's ear to an acoustic stimulus.

BACKGROUND

It is known that the acoustic properties of a user's ear, whether theouter parts (known as the pinna or auricle), the ear canal or both,differ substantially between individuals and can therefore be used as abiometric to identify the user. One or more loudspeakers or similartransducers positioned close to or within the ear generate an acousticstimulus, and one or more microphones similarly positioned close to orwithin the ear detect the acoustic response of the ear to the acousticstimulus. One or more features may be extracted from the responsesignal, and used to characterize an individual.

For example, the ear canal is a resonant system, and therefore onefeature which may be extracted from the response signal is the resonantfrequency of the ear canal. If the measured resonant frequency (i.e. inthe response signal) differs from a stored resonant frequency for theuser, a biometric algorithm coupled to receive and analyse the responsesignal may return a negative result. Other features of the responsesignal may be similarly extracted and used to characterize theindividual. For example, the features may comprise one or more melfrequency cepstrum coefficients. More generally, the transfer functionbetween the acoustic stimulus and the measured response signal (orfeatures of the transfer function) may be determined, and compared to astored transfer function (or stored features of the transfer function)which is characteristic of the user.

One problem associated with ear biometric systems is that the signal tonoise ratio of the measured response signal is typically quite low asthe biometric features of the signal are relatively weak. This problemcan be exacerbated depending on a number of factors. For example, theuser may be present in a noisy environment. For example, earphones usedto acquire the ear biometric data may be poorly fitted to the user's ear(e.g. inserted too far into the user's ear, or not sufficientlyinserted). For example, the bandwidth of the acoustic stimulus may belimited (some audio sources are relatively narrowband). For example, theuser may be generating noise in the canal or headset due to own voice,chewing sounds and handling of the headset.

SUMMARY

According to one aspect of the present disclosure, there is provided amethod operable in a biometric authentication system, the methodcomprising: initiating generation of an acoustic stimulus forapplication to a user's ear; determining a quality measure of a responsesignal to the acoustic stimulus; and responsive to determining that thequality measure is inadequate for performing a biometric process,modifying one or more properties of the acoustic stimulus to improve asignal to noise ratio, SNR, of the response signal.

For example, modifying one or more properties of the acoustic stimulusmay comprise one or more of:

-   -   (i) modifying the gain of the acoustic stimulus;    -   (ii) increasing the duration of the acoustic stimulus;    -   (iii) applying an additional instance of the acoustic stimulus;    -   (iv) shifting the pitch of the acoustic stimulus such that        content of the response signal is better aligned with the user's        ear canal resonances;    -   (v) applying masking noise to the user's ear;    -   (vi) amplifying ambient noise and/or user voice via hear through        mode or sidetone path;    -   (vii) using a masking model to add additional content to the        acoustic stimulus that us inaudible to the user and increasing        the level of the acoustic stimulus;    -   (viii) adding harmonic content to the acoustic stimulus and        increasing the level of the acoustic stimulus; and    -   (ix) adding content to the acoustic stimulus inaudible        frequencies and increasing the level of the acoustic stimulus.

In some embodiments, the method further comprises cancelling the effectof noise from outside the ear on the response signal of the user's earto the acoustic stimulus.

According to another aspect of the present disclosure, there is provideda method operable in a biometric authentication system, the methodcomprising: initiating generation of an acoustic stimulus forapplication to a user's ear; determining a quality measure of a responsesignal to the acoustic stimulus; and responsive to determining that thequality measure is inadequate for performing a biometric process,cancelling the effect of noise from outside the ear on the responsesignal of the user's ear to the acoustic stimulus to improve a signal tonoise ratio, SNR, of the response signal.

For example, cancelling the effect of noise from outside the ear on theresponse signal may comprise cancelling an out-of-ear microphone signalfrom an in-ear microphone signal.

The quality measure may be or comprise one of: an estimatedsignal-to-noise, SNR, of the response signal, an estimated signal levelof the response signal, and an estimated noise level of the responsesignal.

In some embodiments, determining that the quality measure is inadequatecomprises comparing the response signal to one or more of: (i) apre-determined ear canal response of the user; and (ii) hearingcharacteristics of the user. In some embodiments, determining that thequality measure is inadequate may comprise determining masked signallevels of the response signal at one or more frequencies, wherein themasked signal levels correspond with signal levels of the acousticstimulus that are inaudible to the user. In some embodiments,determining that the quality measure is inadequate may comprisecomparing one or more parameters associated with quality of the responsesignal to one or more corresponding parameters extracted from apre-determined ear canal response of the user. In some embodiments,determining that the quality measure is inadequate for performing abiometric process may comprise comparing the quality measure with atarget quality measure.

The method may further comprise responsive to determining that adifference between the determined quality measure and the target qualitymeasure is positive and greater than a threshold gain metric, reducingthe gain of the acoustic stimulus and responsive to determining that thedifference between the determined quality measure and the target qualitymeasure is negative and greater than a threshold gain metric, increasingthe gain of the acoustic stimulus.

In some embodiments, determining the quality measure may comprisedetermining a noise level indicative of a noise level in the user's ear.The noise level may be a predefined value. Alternatively, determiningthe noise level in the user's ear may comprise determining an in-earsignal when no acoustic stimulus is being applied to the user's ear. Forexample, the in-ear signal is determined once the application of theacoustic stimulus has stopped. Determining the noise level in the user'sear may comprise determining an in-ear signal when the acoustic stimulusis being applied to the user's ear. Determining the noise level in theuser's ear may further comprise cancelling the acoustic stimulus fromthe in-ear signal. Determining the noise level in the user's ear maycomprise determining the noise level in the user's ear based on anout-of-ear signal when no acoustic stimulus is being applied to theuser's ear and a transfer function between an ear entrance and aninternal microphone. For example, the out-of-ear signal may bedetermined once the application of the acoustic stimulus has stopped.Determining the noise level in the user's ear may comprise determiningthe noise level in the user's ear based on an out-of-ear signal when theacoustic stimulus is being applied to the user's ear and a transferfunction between an ear entrance and an internal microphone. Determiningthe noise level in the user's ear may further comprise cancelling theacoustic stimulus from the out of-ear signal.

In some embodiments, the method may comprise responsive to determiningone or more of: (i) a relatively high noise situation and (ii) windcondition, determining the noise level in the user's ear based on anin-ear signal. In some embodiments, the method may comprise responsiveto determining one or more of: (i) a relatively low noise situation and(ii) noise from the user's mouth, determining the noise level in theuser's ear based on an out-of-ear signal.

The out-of-ear signal may be derived from an external microphoneexternal to the user's ear. The in-ear signal may be derived from aninternal microphone internal to the user's ear.

Determining the quality measure may comprise determining a signal levelindicative of the response signal. The signal level may be a predefinedvalue. Alternatively, determining the signal level indicative of theresponse signal may comprise analysing the acoustic stimulus andcompensating for the transfer function between the acoustic stimulus anin-ear transducer. In some embodiments, the method may further comprisecompensating for the effects of fit of an earbud comprising thetransducer in the user's ear. Determining the signal level indicative ofthe response signal may comprise determining the response signal of theuser's ear to the acoustic stimulus.

In some embodiments, the method may comprise responsive to determining arelatively high noise situation, cancelling the effect of noise fromoutside the ear on the response signal of the user's ear to the acousticstimulus. In some embodiments, responsive to determining one or more of:(i) a relatively low noise situation and (ii) the transfer function ofthe in-ear transducer being variable, determining the signal levelindicative of the response signal based on the determined responsesignal of the user's ear to the acoustic stimulus.

In some embodiments, the acoustic stimulus may comprise a quiet period,a ramp-up period and a probe period, and determining the quality measuremay comprise determining a noise level from a corresponding quiet periodof the response signal, and determining a signal and noise level from acorresponding probe period of the response signal.

In some embodiments, the acoustic stimulus may comprise non-zerospectral content associated with a first set of one or more frequencyranges and zero spectral content associated with a second set of one ormore frequency ranges and determining the quality measure may comprisedetermining a noise level from the response signal at the second set ofone or more frequency ranges, and determining a signal and noise levelfrom the response signal at the first set of one or more frequencyranges.

In some embodiments, the method further comprises responsive todetermining that the quality measure is adequate for performing thebiometric process, extracting one or more features from the measuredresponse to perform the biometric process. The biometric process may bea biometric authentication process or a biometric enrolment process oran on-ear detection process or an in-ear detection process.

The acoustic stimulus may be pre-recorded audio or streamed audio.

According to another aspect of the present disclosure, there is providedan electronic apparatus, comprising processing circuitry and anon-transitory machine-readable medium storing instructions which, whenexecuted by the processing circuitry, cause the electronic apparatus toimplement any of the described methods.

According to another aspect of the present disclosure, there is provideda non-transitory machine-readable medium storing instructions which,when executed by processing circuitry, cause an electronic apparatus toimplement any of the described methods.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of examples of the present disclosure, and toshow more clearly how the examples may be carried into effect, referencewill now be made, by way of example only, to the following drawings inwhich:

FIGS. 1a to 1e show examples of personal audio devices;

FIG. 2 shows an arrangement according to embodiments of the disclosure;

FIG. 3 shows a system according to embodiments of the disclosure;

FIG. 4A shows an example personal audio device;

FIG. 4B shows a schematic of a signal path through the personal audiodevice of FIG. 4A, according to embodiments of the disclosure;

FIG. 5 is a method according to embodiments of the disclosure;

FIG. 6 is a method according to embodiments of the disclosure;

FIG. 7A is a plot of an acoustic stimulus in the time domain accordingto embodiments of the disclosure;

FIG. 7B is a method according to embodiments of the disclosure; and

FIG. 8A is a plot of variations of acoustic stimulus in the frequencydomain according to embodiments of the disclosure;

FIG. 8B is a method according to embodiments of the disclosure.

DETAILED DESCRIPTION

Embodiments of the disclosure relate to methods, apparatus and systemsfor biometric processes, and particularly to methods, apparatus andsystems for improving biometric processes involving the measuredresponse of a user's ear to an acoustic stimulus.

Described embodiments mitigate poor signal to noise ratio of themeasured response signal by dynamically modifying properties of theacoustic stimulus (for example amplitude, spectral shape, duration) suchthat the signal to noise ratio of the measured response signal issufficiently high to extract desired biometric features with sufficientquality, thereby improving performance of processes, such as biometricprocesses or on-ear detection processes.

As noted above, ear biometric data may be acquired by the generation ofan acoustic stimulus, and the detection of an acoustic response of theear to the acoustic stimulus. One or more features may be extracted fromthe response signal, and used to characterize the individual.

The acoustic stimulus may be generated and the response measured using apersonal audio device. As used herein, the term “personal audio device”is any electronic device which is suitable for, or configurable to,provide audio playback substantially to only a single user. Someexamples of suitable personal audio devices are shown in FIGS. 1a to 1e.

FIG. 1a shows a schematic diagram of a user's ear, comprising the(external) pinna or auricle 12 a, and the (internal) ear canal 12 b. Apersonal audio device 20 comprising a circum-aural headphone is worn bythe user over the ear. The headphone comprises a shell whichsubstantially surrounds and encloses the auricle 12 a, so as to providea physical barrier between the user's ear and the external environment.Cushioning or padding may be provided at an edge of the shell, so as toincrease the comfort of the user, and also the acoustic coupling betweenthe headphone and the user's skin (i.e. to provide a more effectivebarrier between the external environment and the user's ear).

The headphone comprises one or more loudspeakers 22 positioned on aninternal surface of the headphone, and arranged to generate acousticsignals towards the user's ear and particularly the ear canal 12 b. Theheadphone further comprises one or more microphones 24, also positionedon the internal surface of the headphone, arranged to detect acousticsignals within the internal volume defined by the headphone, the auricle12 a and the ear canal 12 b.

The headphone may be able to perform active noise cancellation, toreduce the amount of noise experienced by the user of the headphone.Active noise cancellation operates by detecting a noise (i.e. with amicrophone), and generating a signal (i.e. with a loudspeaker) that hasthe same amplitude as the noise signal but is opposite in phase. Thegenerated signal thus interferes destructively with the noise and solessens the noise experienced by the user. Active noise cancellation mayoperate on the basis of feedback signals, feedforward signals, or acombination of both. Feedforward active noise cancellation utilizes oneor more microphones on an external surface of the headphone, operativeto detect the environmental noise before it reaches the user's ear. Thedetected noise is processed quickly, and the cancellation signalgenerated so as to match the incoming noise as it arrives at the user'sear. Feedback active noise cancellation utilizes one or more errormicrophones positioned on the internal surface of the headphone,operative to detect the combination of the noise and the audio playbacksignal generated by the one or more loudspeakers. This combination isused in a feedback loop, together with knowledge of the audio playbacksignal, to adjust the cancelling signal generated by the loudspeaker andso reduce the noise. The microphone 24 shown in FIG. 1a may thereforeform part of an active noise cancellation system, for example, as anerror microphone.

FIG. 1b shows an alternative personal audio device 30, comprising asupra-aural headphone. The supra-aural headphone does not surround orenclose the user's ear, but rather sits on the auricle 12 a. Theheadphone may comprise a cushion or padding to lessen the impact ofenvironmental noise. As with the circum-aural headphone shown in FIG. 1a, the supra-aural headphone comprises one or more loudspeakers 32 andone or more microphones 34. The loudspeaker(s) 32 and the microphone(s)34 may form part of an active noise cancellation system, with themicrophone 34 serving as an error microphone.

FIG. 1c shows a further alternative personal audio device 40, comprisingan intra-concha headphone (or earphone). In use, the intra-conchaheadphone sits inside the user's concha cavity. The intra-conchaheadphone may fit loosely within the cavity, allowing the flow of airinto and out of the user's ear canal 12 b.

As with the devices shown in FIGS. 1a and 1 b, the intra-conchaheadphone comprises one or more loudspeakers 42 and one or moremicrophones 44, which may form part of an active noise cancellationsystem.

FIG. 1d shows a further alternative personal audio device 50, comprisingan in-ear headphone (or earphone), insert headphone, or ear bud. Thisheadphone is configured to be partially or totally inserted within theear canal 12 b, and may provide a relatively tight seal between the earcanal 12 b and the external environment (i.e. it may be acousticallyclosed or sealed). The headphone may comprise one or more loudspeakers52 and one or more microphones 54, as with the others devices describedabove, and these components may form part of an active noisecancellation system.

As the in-ear headphone may provide a relatively tight acoustic sealaround the ear canal 12 b, external noise (i.e. coming from theenvironment outside) detected by the microphone 54 is likely to be low.

FIG. 1e shows a further alternative personal audio device 60, which is amobile or cellular phone or handset. The handset 60 comprises one ormore loudspeakers 62 for audio playback to the user, and one or moremicrophones 64 which are similarly positioned.

In use, the handset 60 is held close to the user's ear so as to provideaudio playback (e.g. during a call). While a tight acoustic seal is notachieved between the handset 60 and the user's ear, the handset 60 istypically held close enough that an acoustic stimulus applied to the earvia the one or more loudspeakers 62 generates a response from the earwhich can be detected by the one or more microphones 64. As with theother devices, the loudspeaker(s) 62 and microphone(s) 64 may form partof an active noise cancellation system.

All of the personal audio devices described above thus provide audioplayback to substantially a single user in use. Each device comprisesone or more loudspeakers and one or more microphones, which may beutilized to generate biometric data related to the frequency response ofthe user's ear. The loudspeaker is operable to generate an acousticstimulus, or acoustic probing wave, towards the user's ear, and themicrophone is operable to detect and measure a response of the user'sear to the acoustic stimulus, e.g. to measure acoustic waves reflectedfrom the ear canal or the pinna. The acoustic stimulus may be sonic (forexample in the audio frequency range of say 20 Hz to 20 kHz) orultra-sonic (for example greater than 20 kHz or in the range 20 kHz to50 kHz) or near-ultrasonic (for example in the range 15 kHz to 25 kHz)in frequency. In some examples the microphone signal may be processed tomeasure received signals of the same frequency as that transmitted.

Another biometric marker may comprise otoacoustic noises emitted by thecochlear in response to the acoustic stimulus waveform. The otoacousticresponse may comprise a mix of the frequencies in the input waveform.For example, if the input acoustic stimulus consists of two tones atfrequencies f1 and f2, the otoacoustic emission may include a componentat frequency 2*f1−f2. The relative power of frequency components of theemitted waveform has been shown to be a useful biometric indicator. Insome examples therefore the acoustic stimulus may comprise tones of twoor more frequencies and the amplitude of mixing products at sums ordifferences of integer-multiple frequencies generated by otoacousticemissions from the cochlear may be measured. Alternatively, otoacousticemissions may be stimulated and measured by using stimulus waveformscomprising fast transients, e.g. clicks.

Depending on the construction and usage of the personal audio device,the measured response may comprise user-specific components, i.e.biometric data relating to the auricle 12 a, the ear canal 12 b, or acombination of both the auricle 12 a and the ear canal 12 b. Forexample, the circum- aural headphones shown in FIG. 1a will generallyacquire data relating to the auricle 12 a and potentially also the earcanal 12 b. The insert headphones shown in FIG. 1d will generallyacquire data relating only to the ear canal 12 b.

One or more of the personal audio devices described above (or rather,the microphones within those devices) may be operable to detectbone-conducted voice signals from the user. That is, as the user speaks,sound is projected away from the user's mouth through the air. However,acoustic vibrations will also be carried through part of the user'sskeleton or skull, such as the jaw bone. These acoustic vibrations maybe coupled to the ear canal 12 b through the jaw or some other part ofthe user's skeleton or skull, and detected by the microphone. Lowerfrequency sounds tend to experience a stronger coupling than higherfrequency sounds, and voiced speech (i.e. that speech or those phonemesgenerated while the vocal cords are vibrating) is coupled more stronglyvia bone conduction than unvoiced speech (i.e. that speech or thosephonemes generated while the vocal cords are not vibrating). The in-earheadphone 50 may be particularly suited to detecting bone-conductedspeech owing to the tight acoustic coupling around the ear canal 12 b.

All of the devices shown in FIGS. 1a to 1e and described above may beused to implement aspects of the disclosure.

FIG. 2 shows an arrangement 200 according to embodiments of thedisclosure. The arrangement 200 comprises a personal audio device 202and a biometric system 204. The personal audio device 202 may be anydevice which is suitable for, or configurable to provide audio playbackto substantially a single user. The personal audio device 202 generallycomprises one or more loudspeakers, and one or more microphones which,in use, are positioned adjacent to or within a user's ear. The personalaudio device 202 may be wearable, and comprise headphones for each ofthe user's ears. Alternatively, the personal audio device 202 may beoperable to be carried by the user, and held adjacent to the user's earor ears during use. The personal audio device 202 may compriseheadphones or a mobile phone handset, as described above with respect toany of FIGS. 1a to 1 e. The biometric system 204 may, in someembodiments, form part of the personal audio device 202 itself.Alternatively, the system 204 may form part of an electronic host device(e.g. an audio player) to which the personal audio device 202 iscoupled, through wires or wirelessly. In yet further embodiments,operations of the biometric system 204 may be distributed betweencircuitry in the personal audio device 202 and the electronic hostdevice.

The biometric system 204 is coupled to the personal audio device 202 andis operative to control the personal audio device 202 to acquirebiometric data, which is indicative of the individual using the personalaudio device 202.

The personal audio device 202 generates an acoustic stimulus forapplication to the user's ear, and detects or measures the response ofthe ear to the acoustic stimulus. For example, the acoustic stimulus maybe in the sonic range, or ultra-sonic. In some embodiments, the acousticstimulus may have a flat frequency spectrum over a relevant frequencyrange, or be preprocessed in such a way that those frequencies thatallow for a good discrimination between individuals are emphasized (i.e.have a higher amplitude than other frequencies). The measured responsecorresponds to the reflected signal received at the one or moremicrophones, with certain frequencies being reflected at higheramplitudes than other frequencies owing to the particular response ofthe user's ear.

According to embodiments of the disclosure, the personal audio device202 is further operable to determine whether a signal to noise ratio(SNR) of the response signal is adequate for performing a biometricprocess, such as feature extraction for authentication, or on-eardetection. In response to determining that the SNR of the responsesignal is inadequate, the personal audio device 202 may be operable tomodify one or more properties of the acoustic stimulus to improve theSNR of the response signal, as discussed in more detail below.

The biometric system 204 may send suitable control signals to thepersonal audio device 202, so as to initiate the acquisition ofbiometric data, and receive data from the personal audio device 202corresponding to the measured response. The biometric system 204 isoperable to extract one or more features from the measured response andutilize those features as part of a biometric process.

The biometric process may determine whether a response measured at thepersonal audio device 202 is a response induced from an ear, to therebydetect whether or not a headset, headphone or earphone or the like islocated in or on the ear of a user. Alternatively, the biometric processmay involve biometric enrolment or authentication based on the measuredresponse. Enrolment comprises the acquisition and storage of biometricdata which is characteristic of an individual. In the present context,such stored data may be known as an “ear print”. Authentication(sometimes referred to as verification) comprises the acquisition ofbiometric data from an individual, and the comparison of that data tothe stored ear prints of one or more enrolled or authorised users. Apositive comparison (i.e. a determination that the acquired data matchesor is sufficiently close to a stored ear print) results in theindividual being authenticated. For example, the individual may bepermitted to carry out a restricted action, or granted access to arestricted area or device. A negative comparison (i.e. a determinationthat the acquired data does not match or is not sufficiently close to astored ear print) results in the individual not being authenticated. Forexample, the individual may not be permitted to carry out the restrictedaction, or granted access to the restricted area or device.

FIG. 3 shows a system 300 according to embodiments of the disclosure.

The system 300 comprises processing circuitry 322, which may compriseone or more processors, such as a central processing unit or anapplications processor (AP), or a digital signal processor (DSP).

The one or more processors may perform methods as described herein onthe basis of data and program instructions stored in memory 324. Memory324 may be provided as a single component or as multiple components orco-integrated with at least some of processing circuitry 322.Specifically, the methods described herein can be performed inprocessing circuitry 322 by executing instructions that are stored innon-transient form in the memory 324, with the program instructionsbeing stored either during manufacture of the system 300 or personalaudio device 202 or by upload while the system or device is in use.

The processing circuitry 322 comprises a stimulus generator module 303,which is coupled directly or indirectly to an amplifier 304, which inturn is coupled to a loudspeaker 306. The stimulus generator module 303generates an electrical audio signal and provides the electrical audiosignal to the amplifier 304, which amplifies it and provides theamplified signal to the loudspeaker 306. The loudspeaker 306 generates acorresponding acoustic signal, which is output to the user's ear (orears). The audio signal may be sonic or ultra-sonic, for example. Theaudio signal may have a flat frequency spectrum, or be preprocessed insuch a way that those frequencies that allow for a good discriminationbetween individuals are emphasized (i.e. have a higher amplitude thanother frequencies).

As noted above, the audio signal may be output to all or a part of theuser's ear (i.e. the auricle 12 a or the ear canal 12 b of the user asdescribed with reference to FIGS. 1a to 1e ). With the personal device202 fitted to the user's ear, the audio signal is reflected off the ear,and the reflected signal (or echo signal) is detected and received by amicrophone 308. The reflected signal thus comprises data, which ischaracteristic not only of an ear in general, but more specifically ofthe individual's ear. The reflected signal is thus suitable for use as abiometric, either to determine that the personal audio device 202 is inor on the user's ear or to determine a specific characteristic of theuser's ear for use in biometric enrolment or authentication.

The reflected signal is passed from the microphone 308 to ananalogue-to-digital converter (ADC) 310, where it is converted from theanalogue domain to the digital domain. Of course, in alternativeembodiments the microphone 308 may be a digital microphone and produce adigital data signal (which does not therefore require conversion to thedigital domain).

The signal is detected by the microphone 308 in the time domain. Thefeatures extracted for the purposes of the biometric process may be inthe time domain. However, in some embodiments, the features extractedfor the purposes of the biometric process may be in the frequency domain(in that it is the frequency response of the ear which ischaracteristic). The system 300 may therefore comprise a Fouriertransform module 312, which converts the reflected signal to thefrequency domain. For example, the Fourier transform module 312 mayimplement a fast Fourier transform (FFT).

The system 300 may further comprise a microphone 330, and associated ananalogue-to-digital converter (ADC) 332 where necessary. The microphone330 may be an external or out-of-ear microphone, which may be used fornoise signal determinations, for example, as discussed in more detailbelow.

The transformed signal is then passed to a feature extract module 314,which extracts one or more features of the transformed signal for use ina biometric process (e.g. biometric enrolment, biometric authentication,on-ear detect (OED), in-ear detect, etc). For example, the featureextract module 314 may extract the resonant frequency of the user's ear.For example, the feature extract module 314 may extract one or more melfrequency cepstrum coefficients. Alternatively, the feature extractmodule 314 may determine the frequency response of the user's ear at oneor more predetermined frequencies, or across one or more ranges offrequencies.

The extracted feature(s) are passed to a biometric module 316, whichperforms a biometric process on them. For example, the biometric module316 may determine whether the extracted features(s) indicate that thesignal received at the microphone 308 contains a reflection from an earin general, as opposed to open space for example. One or more extractedfeature(s) may be compared to corresponding features in a stored earprint 318. The stored ear print 318 may in the instance be a generic earprint representative of the general population. In another example, thebiometric module 316 may perform a biometric enrolment, in which theextracted features (or parameters derived therefrom) are stored as partof biometric data 318, which is characteristic of the individual (i.e.as an ear print). The biometric data 318 may be stored within the system300 or remote from the system 300 (and accessible securely by thebiometric module 316). In another example, the biometric module 316 mayperform a biometric authentication, and compare the one or more extractfeatures to corresponding features in a stored ear print 318 (ormultiple stored ear prints). In this example, the stored ear print 318may comprise ear prints obtained specifically from authorised users, forexample during biometric enrolment. Again, the stored ear print 318 maybe stored within the system 300 or remote from the system 300 (andaccessible securely by the biometric module 316).

The biometric module 316 generates a biometric result (which may be thesuccessful or unsuccessful generation of an ear print, and/or thesuccessful or unsuccessful authentication and/or the successful orunsuccessful detection of an ear for the purposes of on-ear or in-eardetect). The biometric module 316 may then output the result to controlmodule 302.

In some embodiments the stimulus waveforms may be tones of predeterminedfrequency and amplitude. In other embodiments the stimulus generator 303may be configurable to apply music to the loudspeaker 306, e.g. normalplayback operation, and the feature extract module may be configurableto extract the response or transfer function from whatever signalcomponents the stimulus waveform contains.

Thus in some embodiments the feature extract module 314 may be designedwith foreknowledge of the nature of the stimulus, for example knowingthe spectrum of the applied stimulus signal, so that the response ortransfer function may be appropriately normalised. In other embodimentsthe feature extract module 314 may comprise a second input to monitorthe stimulus (e.g. playback music) and hence provide the feature extractmodule 314 with information about the stimulus signal or its spectrum sothat the feature extract module 314 may calculate the transfer functionfrom the stimulus waveform stimulus to received acoustic waveform fromwhich it may derive the desired feature parameters. In the latter case,the stimulus signal may also pass to the feature extract module 314 viathe FFT module 312.

According to embodiments of the disclosure, the system 300 furthercomprises a quality measure module 326, which is operative to determinethe quality of a response signal to an acoustic stimulus. For example,the quality measure module 326 may determine an estimatedsignal-to-noise ratio, SNR, of the response signal, an estimated signallevel and/or an estimated noise level associated with the responsesignal.

The system 300 further comprises a decision module 328, which isoperative to determine whether the determined quality measure isadequate or inadequate for performing a biometric process, such asfeature extraction for authentication, or on-ear detection. In responseto determining that the quality measure of the response signal isinadequate, the decision module 328 is operable to instruct the controlmodule 302 to modify one or more properties of the acoustic stimulus toimprove the SNR of the response signal. Alternatively, or in addition,the decision module 328 may be operable to instruct the control module302 to cancel the effect of noise from outside the ear on the responsesignal of the user's ear to the acoustic stimulus to improve the SNR ofthe response signal.

The acoustic stimulus may be known, for example, may be based on apre-recorded sound, or may be unknown, for example, may be based onstreamed sound. The acoustic stimulus may have a defined duration or maybe continuous.

In some embodiments, where the acoustic stimulus is based on apre-recorded sound, the quality measure module 326 may determine theresponse signal or more specifically, the response signal level, byanalysing the acoustic stimulus and compensating for a transfer functionbetween the acoustic stimulus and an in-ear transducer, such asloudspeaker 306. The quality measure module 326 may compensate for theeffects of fit of a personal audio device comprising the transducerrelative to the user's ear when determining the response signal level.Thus, the determination of the response signal level could be estimatedas a pre-processing step in advance of providing the acoustic stimulusto the user's ear.

Where the acoustic stimulus unknown a priori, for example, is based onstreamed audio, or indeed is known a priori, the quality measure module326 may determine the response signal by analysing the measured orcaptured response signal. For example, this may involve real timeprocessing of the measured response signal.

The quality measure module 326 may determine a noise level from aninternal or external microphone, such as microphone 308 or 330, and/orby analysing the measured response signal to the acoustic signal asdiscussed in more detail below. For example, this may involve real timeprocessing of noise signals and/or the measured response signal.

In some embodiments, the quality measure module 326 determines a SNRmetric, which may be based on: (i) measured signal and noise levels;(ii) a measured signal level and an assumed constant or predefined noiselevel or (iii) an estimated or measured noise level and an assumedconstant or predefined signal level.

The quality measure module 326 may be coupled to receive signalscorresponding to the output of one or more of: the microphone 308; themicrophone 330; the ADC 310, the Fourier transform module 312; and thefeature extract module 314; and to determine a SNR of a response signalassociated with the acoustic stimulus.

The quality measure module 326 provides a quality measure or metric tothe decision module 328, which determines whether the response signal,based on the determined quality metric, is inadequate for performing abiometric process. For example, the decision module 328 may determinewhether the response signal is adequate to perform a biometric process,such as feature extraction for authentication or on ear detection, basedon a determination of one or more of: the signal level, the noise leveland the SNR.

In some embodiments, the decision module 328 may determine whether ornot the quality measure is adequate by comparing the quality measurewith a target measure, and responsive to determining that the qualitymeasure is less than the target quality measure, modifying one or moreproperties of the acoustic stimulus, or cancel the effect of noise fromoutside the ear on the response signal. For example, where the qualitymeasure is SNR, the decision module 328 may reduce the gain of theacoustic stimulus if it is determined that a difference between thedetermined SNR and the target SNR is positive and greater than athreshold gain metric, and may increase the gain of the acousticstimulus if it is determined that the difference between the determinedSNR and the target SNR is negative and greater than a threshold gainmetric.

The decision module 328 may determine that the quality measure isinadequate by comparing the estimated or measured response signal to apre-determined ear canal response of the user and determining that theestimated or measured response signal differs from the pre-determinedear canal response by greater than a threshold value.

The decision module 328 may determine that the quality measure isinadequate by comparing the estimated or measured response signal withhearing characteristics of the user, such as hearing thresholds or anaudiogram.

The decision module 328 may determine masked signal levels of theresponse signal at one or more frequencies, wherein the masked signallevels correspond with signal levels of the acoustic stimulus that areinaudible to the user.

The decision module 328 may determine whether or not the quality measureis inadequate by comparing one or more parameters associated withquality of the response signal to one or more corresponding parametersextracted from a pre-determined ear canal response of the user.

In some embodiments, the decision module 328 outputs an indication tothe control module 302 to modify one or more properties of the acousticstimulus to improve the SNR of the response signal. In response toreceiving the indication from the decision module, 328, the controlmodule 302 modifies one or more properties of the acoustic stimulus.

The control module 302 may modify the gain of the acoustic stimulus. Forexample, the control module 302 may add additional content to theacoustic stimulus that is inaudible to the user, such as by using amasking model, and increase the level of the acoustic stimulus. Thecontrol module 302 may add harmonic content to the acoustic stimulus andincrease the level of the acoustic stimulus. The control module 302 mayadd content to the acoustic stimulus inaudible frequencies and increasethe level of the acoustic stimulus.

The control module 302 may modify the duration of the acoustic stimulus.For example, the control module 302 may increase the duration of theacoustic stimulus. In some embodiments, the control module 302 may applyor play an additional instance of the acoustic stimulus

In some embodiments, the control module 302 may shift the pitch of theacoustic stimulus such that content of the response signal is betteraligned with the user's ear canal resonances. For example, a user's earcanal response may be analysed using a broadband stimulus and dataindicative of the stored user's ear canal resonances during enrolment ofthe user in the biometric system 300.

In some embodiments, the control module 302 may cancel the effect ofnoise from outside the ear on the response signal of the user's ear tothe acoustic stimulus, for example, when it is determined that the useris in a relatively high noise situation.

The control module 302 may apply masking noise to the user's ear. Forexample, the masking noise may be shaped to match spectral shape of thebackground noise.

The control module 302 may amplify ambient noise and/or user voice viahear through mode or sidetone path.

In some embodiments, alternatively or in addition to outputting anindication to the control module 302 modify one or more properties ofthe acoustic stimulus, the decision module 328 outputs an indication tothe control module 302 to cancel the effect of noise from outside theear on the response signal of the user's ear to the acoustic stimulus,for example, when it is determined that the user is in a relatively highnoise situation and/or there is a significant amount of environmentalnoise in the ear canal.

In some embodiments, the decision module 328 may output an indication asto whether the response signal is adequate for extracting features foruse in the biometric process. In the illustrated embodiment, theindication is output to the feature extract module 314, which can thenhalt extraction a feature extraction process which is already underway,prevent a feature extraction process from being carried out, or alterthe result of a feature extraction process which was previously carriedout. In other embodiments, the indication may be output to the biometricmodule 316 itself, which can then halt a biometric process which isalready underway, prevent a biometric process from being carried out, oralter the result of a biometric process which was previously carriedout. Alternatively, the indication may be output to a separate module,such as the processing circuitry 302 or other module (not illustrated),which ensures that the result of a biometric process is not respected ifthe features are invalidated.

The system 300 may be provided within a personal audio device (such asthe personal audio device 202), or may be distributed across multipledevices. In the former case, all functional blocks other than thespeaker 306 and the microphone 308 may be provided on one or moreintegrated circuits. In the latter case, one or more (or all) of thefunctional blocks other than the speaker 306 and the microphone 308 maybe provided in a host electronic device (e.g. on one or more integratedcircuits). In either case, the microphone may also be co-integrated withone or more functional blocks, such as one or more of the ADC 310, theFourier transform module 312, and the feature extract module 314.

FIG. 4A shows an example personal audio device 402 and FIG. 4B shows aschematic of a signal path through the personal audio device 402. Asillustrated, the personal audio device 402 comprises an out-of-ear(noise) microphone 404, an in-ear microphone 406, an acoustic stimulusgenerator 408 and a transducer 410, the acoustic stimulus generator 408configured to provide a generated acoustic stimulus to the transducer410, and an out-of-ear (voice) microphone 412. As shown, the personalaudio device 402 may also include a voltmeter 414 and an ammeter 416 fordetermining transducer voltage and current measurements and anaccelerometer 418.

Referring to FIG. 4B, F1 represents a transfer function between theacoustic stimulus generator 408 and the out-of-ear microphone 404, F2and F4 represent a transfer function between the acoustic stimulusgenerator 408 and the in-ear microphone 406, F3 represents a transferfunction between the out-of-ear microphone 404 and the in-ear microphone406.

As discussed above, the quality measure module 326 may be configured todetermine or estimate a quality measure of the response signal bydetermining one or more of: a signal level indicative of the responsesignal and a noise level indicative of a noise level in the user's ear.

In some embodiments, the quality measure module 326 may determine thenoise level in the user's ear by determining an in-ear signal when noacoustic stimulus is being applied to the user's ear. For example, thequality measure module 326 may receive an in-ear signal from the in-earmicrophone 406 (arranged to be positioned internal to the user's ear).In some embodiments, the in-ear signal may be determined as the noisesignal once the application of the acoustic stimulus by the acousticstimulus generator 408 has stopped.

In some embodiments, the quality measure module 326 may determine thenoise level in the user's ear by determining an in-ear signal when theacoustic stimulus is being applied to the user's ear. For example, thequality measure module 326 may receive an in-ear signal from the in-earmicrophone 406 (arranged to be positioned internal to the user's ear).In some embodiments, the acoustic stimulus is first cancelled from thein-ear signal to obtain a better estimate of the noise level.

In some embodiments, the quality measure module 326 may determine thenoise level in the user's ear based on an out-of-ear signal when noacoustic stimulus is being applied to the user's ear, such as fromout-of-ear microphone 404 (arranged to be positioned external to theuser's ear), and the transfer function between an ear entrance and aninternal microphone (passive loss), F3. For example, this transferfunction may be determined by cancelling the out-of-ear microphonesignal from the in-ear microphone signal, or by subtracting the spectrumof out-of-ear mic from the in-ear-mic. The quality measure module 326may determine the out-of-ear signal once the application of the acousticstimulus has stopped.

In some embodiments, the quality measure module 326 may determine thenoise level in the user's ear based on an out-of-ear signal when theacoustic stimulus is being applied to the user's ear, such as fromout-of-ear microphone 404 (arranged to be positioned external to theuser's ear), and the transfer function between an ear entrance and aninternal microphone (passive loss), F3. For example, this transferfunction may be determined by cancelling the out-of-ear microphonesignal from the in-ear microphone signal, or by subtracting the spectrumof out-of-ear mic from the in-ear-mic. In some embodiments, the acousticstimulus is first cancelled from the out-of-ear signal to obtain abetter estimate of the noise level.

According to some embodiments, the quality measure module 326 maydetermine the noise level based on the in-ear signal or on theout-of-ear signal depending on whether certain conditions are deemed toapply. For example, if the user is in a relatively high noise situationand/or there is a lot of wind present, which may for example be flaggedto the quality measure module 326 from a noise or wind detector (notshown), the quality measure module 326 may select to determine theuser's ear based on the in-ear signal. On the other hand, if theacoustic stimulus is playing and/or the user is in a relatively lownoise situation and/or noise is determined as coming from the user'smouth, for example, via a voice activity detector, the quality measuremodule 326 may select to determine the user's ear based on theout-of-ear signal.

The quality measure module 326 may determine the signal level indicativeof the response signal by analysing the acoustic stimulus to be appliedand compensating for the transfer function between the acoustic stimulusan in-ear transducer (F2/F4), for example, as a pre-processing step inadvance of providing the acoustic stimulus to the user's ear. Thetransfer function may for example, be derived at design time or may becomputed at run time. In some embodiments, the quality measure module326, may determine the response signal by analysing the measured orcaptured response signal, for example, in real time.

In some embodiments, if the quality measure module 326 determines thatthe user is in a relatively low noise situation, or that the transferfunction of the in-ear transducer is likely to be variable, for example,due to a poor fit of the personal audio device 202 to the user's ear,the quality measure module 326 may select to determine the signal levelindicative of the response signal based on the measured response signalof the user's ear to the acoustic stimulus.

FIG. 5 is a method 500 according to embodiments of the disclosure. Themethod 500 may be carried out in a biometric system, such as thepersonal audio device 202, the system 204 or the system 300.

At 502, the system 202, 204, 300 initiates generation of an acousticstimulus towards a user's ear. The stimulus may be directed towards theouter part of the ear (i.e. the auricle), the ear canal, or both.

At 504, the system 202, 204, 300 determines a quality measure of aresponse signal to the acoustic stimulus.

At 506, the system 202, 204, 300 modifies one or more properties of theacoustic stimulus and/or cancels the effect of noise from outside theear on the response signal in response to determining that the qualitymeasure is inadequate for performing a biometric process.

Referring now to FIG. 6, there is shown a method 600 according toembodiments of the disclosure. The method 600 may be carried out in abiometric system, such as the personal audio device 202, the system 204or the system 300.

At 602, the system 202, 204, 300 initiates generation of an acousticstimulus towards a user's ear. The stimulus may be directed towards theouter part of the ear (i.e. the auricle), the ear canal, or both. Thestimulus may be associated with a duration T_(p) and a level G_(p). Theduration T_(p) and a level G_(p) may be controlled by respectiveduration control and gain control components of the control module 302.The acoustic stimulus may be applied to the user's ear using loudspeaker306.

At 604, the system 202, 204, 300 determines a response signal M_(i) tothe acoustic stimulus indicative of the signal level S. The responsesignal may be captured by in-ear microphone 308, for example.

At 606, the system 202, 204, 300 determines a noise signal M_(e)indicative of background noise N. The background noise may be capturedby out-of-ear microphone 330, for example. The system 202, 204, 300 maybe configured to capture the response signal M_(i) and the noise signalM_(e) substantially synchronously.

At 608, the system 202, 204, 300 determines a SNR based on the signallevel and the noise level. For example, the SNR may be calculated as:

SNR=M _(i) /M _(e)

At 610, the system 202, 204, 300 determines a difference dSNR betweenthe determined SNR and a target SNR.

At 612, the system 202, 204, 300 determines a new gain value G_(pnew),based on the difference dSNR. For example, the difference dSNR may beinput to the gain control component of the control module 302 by thedecision module 328 and the gain control component may determine the newgain value G_(pnew).

At 614, the system 202, 204, 300 determines a new duration valueL_(pnew), based on the difference dSNR. For example, the difference dSNRmay be input to the duration control component of the control module 302by the decision module 328 and the duration control component maydetermine the new duration value L_(pnew).

At 614, the system 202, 204, 300 applies the new gain value G_(pnew) tothe electrical audio signal at a gain module, such as the amplifier 304,to increase the signal level M_(i). The new gain value G_(pnew) may beexponentially smoothed. In some embodiments, where the difference dSNRis positive and greater than a threshold gain metric, the gain G_(p) ofthe acoustic stimulus is reduced and where the difference dSNR isnegative and greater than a threshold gain metric, the gain G_(p) of theacoustic stimulus is increased.

At 616, the system 202, 204, 300 inputs the new duration value L_(pnew)to the acoustic stimulus generator 303 to change the stimulus duration.For example, to increase SNR, the duration value is increased. In someembodiments, the system 202, 204, 300 increases the durationincrementally.

In some embodiments, both the signal level and noise level may bedetermined from the acoustic stimulus, thereby requiring use of only onemicrophone 308, as discussed below with reference to FIGS. 7A and 7B andFIGS. 8A and 8B.

As illustrated in FIG. 7A, the acoustic stimulus or probe may comprisemultiple distinct periods which may be used to determine the signallevel and noise level. For example, the acoustic stimulus may comprise arelatively quiet period, which may be used for noise level estimation, aramp up period to avoid transients, and a probe period, which may beused for noise level estimation.

Referring now to FIG. 7B, there is shown a method 700 according toembodiments of the disclosure. The method 700 may be carried out in abiometric system, such as the personal audio device 202, the system 204or the system 300.

At 702, the system 202, 204, 300 initiates generation of an acousticstimulus towards a user's ear. The stimulus may be directed towards theouter part of the ear (i.e. the auricle), the ear canal, or both. Thestimulus may be associated with a duration T_(p) and a level G_(p). Theduration T_(p) and a level G_(p) may be controlled by respectiveduration control and gain control components of the control module 302.The acoustic stimulus may be applied to the user's ear using loudspeaker306.

At 704, the system 202, 204, 300 determines a response signal M_(i) overduration of the acoustic stimulus. The response signal may be capturedby in-ear microphone 308, for example.

At 706, the system 202, 204, 300 determines a noise level N byintegrating the response signal M_(i) over the duration corresponding tothe quiet period of acoustic stimulus.

At 708, the system 202, 204, 300 determines a signal and noise level,S+N, by integrating the response signal M_(i) over the duration of theacoustic stimulus. Integrating the response signal M_(i) will cause thesignal level to be increased while averaging out the noise.

At 710, the system 202, 204, 300 determines the SNR based on the signaland noise level and the noise level. For example, the SNR may becalculated as:

SNR=((S+N)/N)−1;

The remaining steps of method 700 (712 to 720) correspond with steps 610to 618.

As illustrated in FIG. 8A, the acoustic stimulus or probe may comprisemultiple distinct frequency ranges which may be used to determine thesignal level and noise level. For example, the acoustic stimulus maycomprise non-zero spectral content spanned by one or more frequencyranges, for example, frequencies between F_(start) and F_(end), whichmay be used for noise signal level estimation. Similarly, the acousticstimulus may comprise zero or substantially empty spectral contentspanned by one or more frequency ranges, for example, frequenciesoutside of F_(start) and F_(end), which may be used for noise levelestimation.

Referring now to FIG. 8B, there is shown a method 800 according toembodiments of the disclosure. The method 800 may be carried out in abiometric system, such as the personal audio device 202, the system 204or the system 300.

At 802, the system 202, 204, 300 initiates generation of an acousticstimulus towards a user's ear. The stimulus may be directed towards theouter part of the ear (i.e. the auricle), the ear canal, or both. Thestimulus may be associated with a duration T_(p) and a level G_(p). Theduration T_(p) and a level G_(p) may be controlled by respectiveduration control and gain control components of the control module 302.The acoustic stimulus may be applied to the user's ear using loudspeaker306.

At 804, the system 202, 204, 300 determines a response signal M_(i) overduration of the acoustic stimulus. The response signal may be capturedby in-ear microphone 308, for example.

At 806, the system 202, 204, 300 determines a noise level N byintegrating the response signal M_(i) over the frequency range(s)corresponding to the empty spectral content of the acoustic stimulus.

At 808, the system 202, 204, 300 determines a signal and noise level,S+N, by integrating the response signal M_(i) over the frequencyrange(s) corresponding to the non-zero spectral content of the acousticstimulus. Integrating the response signal M_(i) will cause the signallevel to be increased while averaging out the noise.

At 810, the system 202, 204, 300 determines the SNR based on the signaland noise level and the noise level. For example, the SNR may becalculated as:

SNR=((S+N)/N)−1;

The remaining steps of method 800 (812 to 820) correspond with steps 610to 618.

Thus, systems, apparatus and methods are provided for use in an earbiometric system which considers the SNR of the measured response signalin order to assess whether the measured response signal is suitable oradequate for performing a biometric process.

Embodiments may be implemented in an electronic, portable and/or batterypowered host device such as a smartphone, an audio player, a mobile orcellular phone, a handset. Embodiments may be implemented on one or moreintegrated circuits provided within such a host device. Embodiments maybe implemented in a personal audio device configurable to provide audioplayback to a single person, such as a smartphone, a mobile or cellularphone, headphones, earphones, etc. See FIGS. 1a to 1 e. Again,embodiments may be implemented on one or more integrated circuitsprovided within such a personal audio device. In yet furtheralternatives, embodiments may be implemented in a combination of a hostdevice and a personal audio device. For example, embodiments may beimplemented in one or more integrated circuits provided within thepersonal audio device, and one or more integrated circuits providedwithin the host device.

It should be understood—especially by those having ordinary skill in theart with the benefit of this disclosure—that that the various operationsdescribed herein, particularly in connection with the figures, may beimplemented by other circuitry or other hardware components. The orderin which each operation of a given method is performed may be changed,and various elements of the systems illustrated herein may be added,reordered, combined, omitted, modified, etc. It is intended that thisdisclosure embrace all such modifications and changes and, accordingly,the above description should be regarded in an illustrative rather thana restrictive sense.

Similarly, although this disclosure makes reference to specificembodiments, certain modifications and changes can be made to thoseembodiments without departing from the scope and coverage of thisdisclosure. Moreover, any benefits, advantages, or solutions to problemsthat are described herein with regard to specific embodiments are notintended to be construed as a critical, required, or essential featureor element.

Further embodiments and implementations likewise, with the benefit ofthis disclosure, will be apparent to those having ordinary skill in theart, and such embodiments should be deemed as being encompassed herein.Further, those having ordinary skill in the art will recognize thatvarious equivalent techniques may be applied in lieu of, or inconjunction with, the discussed embodiments, and all such equivalentsshould be deemed as being encompassed by the present disclosure.

The skilled person will recognise that some aspects of theabove-described apparatus and methods, for example the discovery andconfiguration methods may be embodied as processor control code, forexample on a non-volatile carrier medium such as a disk, CD- or DVD-ROM,programmed memory such as read only memory (Firmware), or on a datacarrier such as an optical or electrical signal carrier. For manyapplications embodiments of the invention will be implemented on a DSP(Digital Signal Processor), ASIC (Application Specific IntegratedCircuit) or FPGA (Field Programmable Gate Array). Thus the code maycomprise conventional program code or microcode or, for example code forsetting up or controlling an ASIC or FPGA. The code may also comprisecode for dynamically configuring re-configurable apparatus such asre-programmable logic gate arrays. Similarly, the code may comprise codefor a hardware description language such as Verilog™ or VHDL (Very highspeed integrated circuit Hardware Description Language). As the skilledperson will appreciate, the code may be distributed between a pluralityof coupled components in communication with one another. Whereappropriate, the embodiments may also be implemented using code runningon a field-(re)programmable analogue array or similar device in order toconfigure analogue hardware.

Note that as used herein the term module shall be used to refer to afunctional unit or block which may be implemented at least partly bydedicated hardware components such as custom defined circuitry and/or atleast partly be implemented by one or more software processors orappropriate code running on a suitable general purpose processor or thelike. A module may itself comprise other modules or functional units. Amodule may be provided by multiple components or sub-modules which neednot be co-located and could be provided on different integrated circuitsand/or running on different processors.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims or embodiments. The word “comprising”does not exclude the presence of elements or steps other than thoselisted in a claim or embodiment, “a” or “an” does not exclude aplurality, and a single feature or other unit may fulfil the functionsof several units recited in the claims or embodiments. Any referencenumerals or labels in the claims or embodiments shall not be construedso as to limit their scope.

As used herein, when two or more elements are referred to as “coupled”to one another, such term indicates that such two or more elements arein electronic communication or mechanical communication, as applicable,whether connected indirectly or directly, with or without interveningelements.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the example embodiments herein that aperson having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. Moreover, reference in the appended claims to an apparatusor system or a component of an apparatus or system being adapted to,arranged to, capable of, configured to, enabled to, operable to, oroperative to perform a particular function encompasses that apparatus,system, or component, whether or not it or that particular function isactivated, turned on, or unlocked, as long as that apparatus, system, orcomponent is so adapted, arranged, capable, configured, enabled,operable, or operative. Accordingly, modifications, additions, oromissions may be made to the systems, apparatuses, and methods describedherein without departing from the scope of the disclosure. For example,the components of the systems and apparatuses may be integrated orseparated. Moreover, the operations of the systems and apparatusesdisclosed herein may be performed by more, fewer, or other componentsand the methods described may include more, fewer, or other steps.Additionally, steps may be performed in any suitable order. As used inthis document, “each” refers to each member of a set or each member of asubset of a set.

Although exemplary embodiments are illustrated in the figures anddescribed below, the principles of the present disclosure may beimplemented using any number of techniques, whether currently known ornot. The present disclosure should in no way be limited to the exemplaryimplementations and techniques illustrated in the drawings and describedabove.

Unless otherwise specifically noted, articles depicted in the drawingsare not necessarily drawn to scale.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the disclosureand the concepts contributed by the inventor to furthering the art, andare construed as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present disclosurehave been described in detail, it should be understood that variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the disclosure.

Although specific advantages have been enumerated above, variousembodiments may include some, none, or all of the enumerated advantages.Additionally, other technical advantages may become readily apparent toone of ordinary skill in the art after review of the foregoing figuresand description.

To aid the Patent Office and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims or claimelements to invoke 35 U.S.C. § 112(f) unless the words “means for” or“step for” are explicitly used in the particular claim.

1. A method operable in a biometric authentication system, the methodcomprising: initiating generation of an acoustic stimulus forapplication to a user's ear; determining a quality measure of a responsesignal to the acoustic stimulus; and responsive to determining that thequality measure is inadequate for performing a biometric process,modifying one or more properties of the acoustic stimulus to improve asignal to noise ratio, SNR, of the response signals wherein determiningthat the quality measure is inadequate for performing a biometricprocess comprises comparing the quality measure with a target qualitymeasure; and wherein responsive to determining that a difference betweenthe determined quality measure and a target quality measure is positiveand greater than a threshold gain metric, reducing the gain of theacoustic stimulus and responsive to determining that the differencebetween the determined quality measure and the target quality measure isnegative and greater than a threshold gain metric, increasing the gainof the acoustic stimulus.
 2. The method of claim 1, wherein modifyingone or more properties of the acoustic stimulus comprises one or moreof: (i) increasing the duration of the acoustic stimulus; (ii) applyingan additional instance of the acoustic stimulus; (iii) shifting thepitch of the acoustic stimulus such that content of the response signalis better aligned with the user's ear canal resonances; (iv) applyingmasking noise to the user's ear; (v) amplifying ambient noise and/oruser voice via hear through mode or sidetone path; (vi) using a maskingmodel to add additional content to the acoustic stimulus that usinaudible to the user and increasing the level of the acoustic stimulus;(vii) adding harmonic content to the acoustic stimulus and increasingthe level of the acoustic stimulus; and (viii) adding content to theacoustic stimulus inaudible frequencies and increasing the level of theacoustic stimulus.
 3. The method of claim 1, further comprisingcancelling the effect of noise from outside the ear on the responsesignal of the user's ear to the acoustic stimulus by cancelling anout-of-ear microphone signal from an in-ear microphone signal. 4.-5.(canceled)
 6. The method of claim 1, wherein the quality measure is oneof: an estimated signal-to-noise, SNR, of the response signal, anestimated signal level of the response signal, and an estimated noiselevel of the response signal.
 7. (canceled)
 8. The method of claim 1,wherein determining that the quality measure is inadequate comprisesdetermining masked signal levels of the response signal at one or morefrequencies, wherein the masked signal levels correspond with signallevels of the acoustic stimulus that are inaudible to the user.
 9. Themethod of claim 1, wherein determining that the quality measure isinadequate comprises comparing one or more parameters associated withquality of the response signal to one or more corresponding parametersextracted from a pre-determined ear canal response of the user. 10.-11.(canceled)
 12. The method of claim 1, wherein determining the qualitymeasure comprises determining a noise level indicative of a noise levelin the user's ear.
 13. (canceled)
 14. The method of claim 12, whereindetermining the noise level in the user's ear comprises one of: (i)determining an in-ear signal when no acoustic stimulus is being appliedto the user's ear, (ii) determining an in-ear signal once theapplication of the acoustic stimulus has stopped, or (iii) determiningan in-ear signal when the acoustic stimulus is being applied to theuser's ear. 15.-16. (canceled)
 17. The method of claim 16, whereindetermining the noise level in the user's ear further comprisingcancelling the acoustic stimulus from the in-ear signal.
 18. The methodof claim 12, wherein determining the noise level in the user's earcomprises determining the noise level in the user's ear based on anout-of-ear signal when no acoustic stimulus is being applied to theuser's ear and a transfer function between an ear entrance and aninternal microphone.
 19. (canceled)
 20. The method of claim 12, whereindetermining the noise level in the user's ear comprises determining thenoise level in the user's ear based on an out-of-ear signal when theacoustic stimulus is being applied to the user's ear and a transferfunction between an ear entrance and an internal microphone.
 21. Themethod of claim 20, wherein determining the noise level in the user'sear further comprising cancelling the acoustic stimulus from the outof-ear signal.
 22. The method of claim 12, wherein responsive todetermining one or more of: (i) a relatively high noise situation and(ii) wind condition, determining the noise level in the user's ear basedon an in-ear signal.
 23. The method of claim 12, wherein responsive todetermining one or more of: (i) a relatively low noise situation and(ii) noise from the user's mouth, determining the noise level in theuser's ear based on an out-of-ear signal.
 24. The method of claim 18,wherein the out-of-ear signal is derived from an external microphoneexternal to the user's ear. 25.-30. (canceled)
 31. The method of claim1, wherein responsive to determining one or more of: (i) a relativelylow noise situation and (ii) a transfer function of the in-eartransducer being variable, determining a t signal level indicative ofthe response signal based on the determined response signal of theuser's ear to the acoustic stimulus.
 32. The method of claim 1, whereinthe acoustic stimulus comprises a quiet period, a ramp-up period and aprobe period, and wherein determining the quality measure comprisesdetermining a noise level from a corresponding quiet period of theresponse signal, and determining a signal and noise level from acorresponding probe period of the response signal.
 33. The method ofclaim 1, wherein the acoustic stimulus comprises non-zero spectralcontent associated with a first set of one or more frequency ranges andzero spectral content associated with a second set of one or morefrequency ranges and wherein determining the quality measure comprisesdetermining a noise level from the response signal at the second set ofone or more frequency ranges, and determining a signal and noise levelfrom the response signal at the first set of one or more frequencyranges. 34.-36. (canceled)
 37. An electronic apparatus, comprisingprocessing circuitry and a non-transitory machine-readable mediumstoring instructions which, when executed by the processing circuitry,cause the electronic apparatus to: initiate generation of an acousticstimulus for application to a user's ear; determine a quality measure ofa response signal to the acoustic stimulus; and responsive todetermining that the quality measure is inadequate for performing abiometric process, modify one or more properties of the acousticstimulus to improve a signal to noise ratio, SNR, of the responsesignal; wherein determining that the quality measure is inadequate forperforming a biometric process comprises comparing the quality measurewith a target quality measure; and wherein responsive to determiningthat a difference between the determined quality measure and a targetquality measure is positive and greater than a threshold gain metric,reduce the gain of the acoustic stimulus and responsive to determiningthat the difference between the determined quality measure and thetarget quality measure is negative and greater than a threshold gainmetric, increase the gain of the acoustic stimulus.
 38. A non-transitorymachine-readable medium storing instructions which, when executed byprocessing circuitry, cause an electronic apparatus to: initiategeneration of an acoustic stimulus for application to a user's ear;determine a quality measure of a response signal to the acousticstimulus; and responsive to determining that the quality measure isinadequate for performing a biometric process, modify one or moreproperties of the acoustic stimulus to improve a signal to noise ratio,SNR, of the response signal; wherein determining that the qualitymeasure is inadequate for performing a biometric process comprisescomparing the quality measure with a target quality measure; and whereinresponsive to determining that a difference between the determinedquality measure and a target quality measure is positive and greaterthan a threshold gain metric, reduce the gain of the acoustic stimulusand responsive to determining that the difference between the determinedquality measure and the target quality measure is negative and greaterthan a threshold gain metric, increase the gain of the acousticstimulus.